In order to understand the object of the invention clearly, it is appropriate to recall that most aircraft comprise either airplanes or rotorcraft.
The term “airplane” is used to designate any aircraft in which lift is provided by at least one fixed wing.
Amongst airplanes, there is a first type of airplane comprising short takeoff and landing airplanes that are provided with a variety of devices seeking to minimize the length of runway needed for landing and taking off, such as high-lift flap devices, for example. That first type of airplane is capable of landing at low speeds of the order of fifty kilometers per hour (km/h).
Although such performance is remarkable, it is not possible to consider landing on and taking off from a small oil platform.
A second known type of airplane comprises airplanes that take off and land vertically. By way of example, mention may be made of the Harrier® jet airplane.
That second type of airplane is indeed capable of landing on an oil platform. Nevertheless, it presents very high fuel consumption, thereby limiting its range and/or its payload.
Known aircraft thus do not appear to be suitable for the need set out above.
Furthermore, the term “rotorcraft” designates any aircraft in which lift is provided in full or in part by one or more propellers of substantially vertical axis and large diameter, referred to as a lift rotor or as a rotary wing.
In the category of rotorcraft, there is the autogyro in which the main rotor is not powered, but rotates in auto-rotation under the effect of the forward speed of the aircraft. Propulsion is provided for example by a propeller having an axis that is substantially horizontal in forward flight and driven by an engine. That formula is not capable of vertical flight, unless the rotor is initially set into rotation by an auxiliary device enabling the rotor to be driven at a faster speed. Under such circumstances, an autogyro cannot hover, but is capable merely of rising or descending following trajectories of very steep slope.
In the category of rotorcraft, there is also the helicopter, having at least one main rotor that is driven by an appropriate engine that serves to provide both lift and propulsion. The helicopter is capable of hovering, i.e. of remaining at a fixed point in three dimensions, is capable of taking off and landing vertically, and is capable of moving in any direction. The vast majority of rotorcraft produced in the world are helicopters.
A helicopter is perfectly capable of landing on an oil platform without difficulty. Nevertheless, the forward speed of a conventional helicopter is low, which prevents it from achieving large ranges and as a result from reaching oil platforms that are far from the shore.
To remedy that, various other novel formulae have been studied to a greater or lesser extent, and some have even given rise to practical embodiments.
In this respect, mention may be made of the compound rotorcraft that takes off and lands like a helicopter, and cruises like an autogyro: its rotor is caused to auto-rotate because of the forward speed of the aircraft and it provides some of its lift, with the remainder being provided by an auxiliary wing, a propeller of substantially horizontal axis delivering the force needed for movement in translation.
The compound rotorcraft is effective but embodiments thereof are often complex and expensive in order to comply with the requirements of the safety standards in force.
The convertible rotorcraft constitutes another particular rotorcraft formula. This term covers any rotorcraft that changes its configuration in flight: takeoff and landing in a helicopter configuration, cruising flight in an airplane configuration, e.g. with two rotors that are tilted through about 90 degrees so that they can act as propellers.
Of those various rotorcraft formulae, the helicopter is the simplest and is therefore the most widespread in spite of the fact that the maximum speed in translation of a helicopter is of the order of 300 km/h, which is low and less than that which can be envisaged by formulae of the combined or convertible type, that are technically more complex and more expensive.
Finally, documents DE 20303024, US 2006/0266879, US 2002/011539, WO 2007/014531, and U.S. Pat. No. 4,469,294 present a variety of aircraft embodiments.
Furthermore, it can be understood that an aircraft that is to provide communication between the shore and an oil platform must be capable of guaranteeing passenger safety under flight conditions that are sometimes difficult.